(1) Field of the Invention
The present invention relates to an improved plasma reactor apparatus, preferably with a tunable and electrodeless radiofrequency wave cavity around a confined space for the plasma, and to a method wherein the apparatus and method are used for treating a substrate with an excited species from the plasma in a reaction chamber spaced from the confined space for the plasma and separated by an aperture or restricted opening through which the plasma passes. In particular the present invention relates to an apparatus wherein the position of the plasma in the confined space is controlled by various means during operation of the apparatus.
(2) Prior Art
Asmussen et al U.S Pat. Nos. 4,507,588; 4,585,668; 4,727,293; 4,630,566; and 4,691,662 describe methods and apparatus for the generation of an electrodeless disk shaped plasma. The method and apparatus of these patents work very well and are utilized in the present invention, as are the more conventional plasmas formed in elongate quartz tubes as shown in Proceedings of the IEEE 62, 109-117 (1974).
The above referenced patents and publication describe the prior art in great detail. In all of this prior art, a sliding short or other tuning means is used to tune microwaves or other radiofrequency waves in a cavity around the plasma confining means. The sliding short is external of the plasma confining means which is non-metallic and transparent to the radiofrequency waves (e.g. quartz). Usually the radiofrequency waves are tuned in the cavity so that the reflected power is zero so that the microwaves are resonant and matched in the cavity. Also, radiofrequency waveguides can be used. In this case, the microwaves are propagating in the waveguide. There is an incident wave and a wave is reflected at the plasma discharge. In contrast, a cavity applicator has a resonant standing wave (higher Q) wave incident on the plasma discharge.
In J. of Propulsion and Power 3, 136-144 (1987) and Applied Physics Lett. 44, 1014-1016 (1984) a propulsion device is described. The apparatus includes a nozzle which is used to develop the thrust using a low molecular weight gas (N.sub.2 or He) at high pressures. There was no mention of the device for any materials processing.
One important use of plasmas is in diamond or diamond-like thin film deposition. Such plasma deposition is described for instance in Cann U.S. Pat. Nos. 4,471,003, 4,682,564 and 4,487,162; Aisenberg U.S. Pat. No. 3,961,103; Venkataramanan et al U.S. Pat. No. 4,647,512; Carlson et al U.S. Pat. No. 4,060,660; Ovshinsky et al U.S. Pat. No. 4,663,183; Etzkorn et al U.S. Pat. No. 4,728,529 and in Kamo et al U.S. Pat. No. 4,434,188 to produce such films. Some of these patents describe plasmas created by DC arc electrodes which contaminate the coating or the like on the substrate. The electrodes also decrease operating life and increase maintenance. Also Kurihara et al Appl. Phys. Lett 52: 437-438 (1988) describe the use of DC arc plasmas for this purpose. Kamo et al describe an electrodeless plasma apparatus which is an improvement. Also, Kamo et al (M. Kamo, Y. Sato, S. Matsumoto, and N. Setaka, Journal of Crystal Growth 62, 642-644 (1983)) show a representative apparatus. Hydrogen and methane are fed into a quartz tube which also contains a substrate on which the diamond film is to be formed. Microwave energy at 2.45 GHz is transmitted to the chamber through a waveguide in order to form a microwave plasma inside the quartz tube. Film growth on the substrate results from chemical vapor deposition as the methane is dissociated into radicals and ions of C and H. With this apparatus, diamond particles were formed on silicon wafers under conditions of 1 to 3% methane, 300 to 700 W of microwave power, and total pressures of approximately 10 to 100 Torr. The substrate reached temperatures of 800.degree. to 1000.degree. C. There is a need for a method and apparatus which is electrodeless and which can produce a diamond or diamond-like coating over a large surface area at high deposition rates.
Matsumoto et al U.S Pat. No. 4,767,608 describes the use of plasmas provided through apertures for depositing diamond thin films. No adjustment of the position or size of the plasma relative to the aperture during operation of the apparatus is described. As a result the apparatus is not as versatile and thus can not be adapted to a wide range of processing conditions.
The properties of diamond include an extremely high degree of hardness, a very high thermal conductivity, optical transparency, high electrical resistivity, and semiconductivity induced by doping with trace levels of impurities. The following is a partial list of diamond film applications: lens coating; laser windows; tribology applications (hard surfaces, long wearing bearings, etc.); electronic packaging and passivation; thermal heat sinks; electrical isolation; high temperature electronic devices; microwave and mm wave power devices; and low noise UV detectors. This unusual combination of properties makes the production of such films highly desirable and a preferred product of the present invention.